A woman moves through a forest of symbols, peopled by liminal obsessives, gathering clues to a conspiratorial mystery. So might you describe Thomas Pynchon's diabolically lean and funny The Crying of Lot 49, perhaps the most perfect American novel of its age. Fitting the same description is the new novel by William Gibson, whose own literary trajectory has seen him develop from noir prophet of cyberspace (the word he coined in Neuromancer, 1984) to a kind of wi-fi'd Pynchon for the present.

The heroine, Hollis, is a former singer for a cult early-1990s indie band, now a journalist. She accepts a commission from an obscure British magazine to interview some LA practitioners of "locative art": installations in public places that are invisible unless you have a VR headset, in which case the virtual performance is overlaid on physical reality. But the tech genius behind the locative installations is also involved in something weirder: arcane data, encoded into the music on iPods, is being smuggled to Cuba and back through an old man who speaks Russian; and much ingenuity is being spent on trying to track a shipping container, flitting from boat to boat at sea for years, whose contents are unknown.

Hollis soon finds out that her magazine assignment is for a publication that may not even exist, but is bankrolled by a cosmically wealthy Swiss advertising mogul named Hubertus Bigend. Readers of Gibson's 2003 novel Pattern Recognition will already know and enjoy Bigend, a marvellously cynical personage, one of whose purposes is to demonstrate that limitless curiosity can be thoroughly amoral. He says things such as "Secrets are the very root of cool", and snacks on "what looked like sushi wrapped in raw meat".

Also somehow involved in the plot are a young Cuban-Chinese man called Tito, who plays keyboards and practises the Russian martial art Systema, whose phenomenology of action Gibson brilliantly delineates through the allegorical device of giving Tito several specialised gods to watch over him. Meanwhile, as Hollis gets mixed up in a crew chasing the shipping container, a merely physical MacGuffin, the novel offers a parallel fiesta of semiological detection through the eyes of Milgrim, a dope addict being used as a Russian translator by a federal agent.

Milgrim often seems to be a repository for Gibson's trademark reverse-engineered metaphors, whereby the physical is imaged as virtual. At one point, looking around a hotel room, he remarks: "The pixels in the cabinet's wood-grain veneer were too large ... you only got the high-resolution stuff in your better places." We are reminded of the first sentence of Neuromancer: "The sky above the port was the colour of television, tuned to a dead channel." But elsewhere, as though Gibson is deliberately playing with his own most famous line, he trades the device for one of melancholy oxidisation: "The world outside the restaurant's windows ... was the colour of a silver coin, misplaced for decades in a drawer."

No need to insist any longer, if, as one character argues, the whole world is already cyberspace. Maybe the past is too, as Milgrim thinks, looking at old photographs of the World Trade Centre: the towers "now seemed ... to have been photoshopped into every image he encountered them in". The novel also addresses aspects of post-9/11 politics: torture in secret prisons, corruption in Iraq spending. We are given to understand that certain ex-CIA types are not happy with developments. A further implication of the novel's title is that "spook country" is the one all Americans live in. As a modern Mephistopheles might have said: "Why, this is spook country, nor am I out of it."

Spooks are spies, but also the persistent dead. Another character thinks about "those ghost-signs, fading high on the windowless sides of blackened buildings, spelling out the names of products made meaningless by time". This is a novel about, and also full of, ghost-signs, or signs that may not be signs, and about the difficulty of telling the difference. Gibson delights in saturating the pages with data that may or may not encode clues for the reader. Does the hexadecimal code for a wi-fi station mean something? What about the phrase "East Van Halen" spraypainted on a dumpster? In this comedy of hermeneutics, the characters play too: "If you knew enough Greek, [Hollis] thought, you could assemble a word that meant divination via the pattern of grease left on a paper plate by broasted potatoes. But it would be a long word."

Gibson's prose continues to gleam with a vivid economy, as though he is trying to find the most suggestively unexpected angle. Here is a man with a "curiously nonreflective simulacrum of Kim Jong-il's jet-black haircut". Here is what it is like to suck on a pill: "He wanted to concentrate fully on that instant when the sublingual tablet phase-shifted from being to not-being." This novel is a political thriller that is also a satire on advertising, music and the geekocracy, a finely machined mystery whose main pleasures lie in its rich store of miniature aesthetic jolts and unexpected textures. Gibson country is still a terrain all its own.